Nutritional Psychiatry: Emerging Evidence and Expert Interview

An inverse association has been identified between healthy dietary patterns and the risk of depression.

Mental illness is a top cause of global disability and the source of significant burden to social, economic, and healthcare systems. The cost of lost productivity due to psychological and related disorders is estimated to approach $8.5 trillion.1 Treatment as usual with medication and psychotherapy is ineffective for a substantial portion of patients–more than 50% of those with major depressive disorder, for example2–indicating the need for alternate prevention and treatment strategies.

“Indeed, recent evidence suggests that despite a substantial increase in the use of psychotropics and wider availability of psychotherapies, the population burden of depression has not reduced, and may be increasing,” according to a review published in the Proceedings of the Nutrition Society.3 “If indeed this is the case, it suggests the presence of operative environmental risk factors for depression.”

A sizeable and increasing body of research in the growing field of nutritional psychiatry supports the role of diet in mental health, as well as its potential as a modifiable risk factor for mental illness. The new review examined evidence from systematic reviews, meta-analyses, clinical trials, and observational studies that have focused on this topic.

Overall, this research has found an inverse association between healthy dietary patterns (those with high intake of fruits, vegetables, whole grains, nuts and seeds, fish, and minimal intake of processed foods) and the risk of depression.4-6 Importantly, these associations are “independent of body weight, suggesting dietary patterns can affect mental illness via pathways that are independent of weight status,” the authors noted.

Such studies have also positively linked depression and anxiety with unhealthy dietary patterns (characterized by frequent consumption of high-fat, high-sugar, processed foods).4,7 Additional findings have observed associations between poor nutrition in utero and in early life with emotional and behavior impairment in childhood.

The most-studied pathways implicated in the connection of diet and mental illness are as follows. Each pathway likely overlaps and interacts with the others.

Chronic low-grade inflammation, such as that caused by lifestyle factors including poor diet, smoking, lack of sleep, and psychological stress, has been observed in individuals with depression, bipolar disorder, and schizophrenia.8-10 In observational studies, dietary patterns that are higher in fruits, vegetables, and polyunsaturated fatty acids–such as the Mediterranean diet–have been linked with lower levels of inflammation, while intervention studies have demonstrated significant improvement in inflammatory markers following adherence to the Mediterranean diet.11,12

Oxidative stress has been shown to be elevated in patients with depression, and this population has also demonstrated lower levels of antioxidants compared with healthy controls. Other research noted increased oxidative stress in patients with schizophrenia. “Given the abundance of antioxidant compounds in foods such as fruit and vegetables, this is a pathway that could be modulated through dietary means,” the authors wrote.

Brain plasticity may be improved through healthy dietary patterns, according to some research. Evidence suggests that neurotrophins such as brain-derived neurotrophic factor (BDNF) mediate hippocampal neurogenesis, and preliminary findings reveal that a 4-week intervention to increase the intake of carotenoid-rich produce led to increased serum BDNF in patients with schizophrenia vs controls. “In addition to possessing antioxidant and anti-inﬂammatory properties, nutrients such as n-3 fatty acids, polyphenols, l-theanine and vitamin E, can also stimulate neurogenesis while energy-dense diets high in fat and sugar impair this process,” the authors stated.

The gastrointestinal microbiota has increasingly been linked with multiple pathways implicated in mental illness, including serotonin transmission, immune function, BDNF modulation, and the hypothalamic-pituitary-adrenal axis-mediated stress response. It may also be a mediating factor in each of the other potential pathways described. It is possible that diet-induced changes in gut microbiota and intestinal permeability could positively or negatively influence mental health.

Mitochondrial dysfunction has been found to be associated with depression, bipolar disorder, and schizophrenia, and animal models indicate that mitochondrial function could be influenced by certain dietary supplements and nutraceuticals, including creatine, resveratrol, coenzyme Q10, and α-lipoic acid.

To learn more about the latest developments in this field, along with clinical implications for mental health professionals, Psychiatry Advisor spoke with one of the authors of the review: Felice Jacka, PhD, researcher and professor of nutritional and epidemiological psychiatry at Deakin University in Australia, founder and director of the Food and Mood Centre there, and founder and president of theInternational Society for Nutritional Psychiatry Research (ISNPR).

Psychiatry Advisor:What is the most compelling evidence supporting an influence of diet quality on mental health?

Dr Jacka: We and others have led many studies showing that the quality of people's diets is linked to their mental health. In particular, whether people choose a diet higher in vegetables, fruits, whole grains, nuts and legumes, fish, and grass-fed meat, or a diet high in processed and junk foods–such as soda, fried and fatty foods, and foods high in refined carbohydrates and added sugars–is linked to their risk for the common mental disorders, depression and anxiety.

These relationships are largely independent of income, education, physical activity, smoking, body weight, and other important factors that might influence diet and mental health. Importantly, these long-term relationships do not appear to be explained by an impact of mental health on dietary habits, although that is also a factor to consider. We see these patterns of associations consistently across the world, in diverse countries and cultures, and–very importantly–across age groups.